The present invention relates to a solenoid valve for controlling a fuel injector of an internal combustion engine according to the definition of the species in claim 1.
Such a solenoid valve, known from German Patent Application 197 08 104 A1, for example, is used to control the fuel pressure in the control pressure chamber of a fuel injector, for example in the injector of a common rail injection system. The movement of a valve plunger, using which an injection opening of the fuel injector is opened or closed, is controlled via the fuel pressure in the control pressure chamber. The known solenoid valve has an electromagnet arranged in a housing part, a movable armature, and a control valve element which is moved using the armature, is acted upon by a closing spring in the closing direction, works together with a valve seat of the solenoid valve and thus controls the fuel discharge out of the control pressure chamber. A known disadvantage of solenoid valves is the armature bounce. When the magnet is switched off, the armature, and with it the control valve element, is accelerated by the closing spring of the solenoid valve toward the valve seat in order to seal off a fuel drain channel out of the control pressure chamber. The impact of the control valve element on the valve seat may result in a disadvantageous oscillation and/or bounce of the control valve element on the valve seat, due to which the control of the injection procedure is impaired. In the solenoid valve known from German Patent Application 197 08 104 A1, the armature is therefore implemented in two parts, having an armature pin and an armature plate mounted so it slides on the armature pin, so that, upon the impact of the control valve element on the valve seat, the armature plate moves further against the tension of a return spring. The return spring subsequently conveys the armature plate back to its starting position against a stop of the armature pin. The effectively braked mass, and therefore the kinetic energy of the armature striking the valve seat, which causes bounce, are reduced through the two-part embodiment of the armature; however, the armature plate may disadvantageously post-oscillate on the armature pin after the solenoid valve is closed.
Since control of the solenoid valve only leads to a defined injection quantity if the armature plate no longer post-oscillates, measures are necessary in order to reduce the post-oscillation of the armature plate. This is particularly necessary to achieve shorter time intervals between, for example, a pre-injection and a main injection. To achieve this object, the related art uses a damping device which includes a stationary part and a part moved using the armature plate. The stationary part is formed by an overtravel stop which delimits the maximum path length by which the armature plate may move on the armature pin. The movable part is formed by a projection of the armature plate facing the stationary part.
The overtravel stop may be formed by the face of a slider which guides the armature pin and is fixedly clamped in the housing of the solenoid valve or by a part mounted in front of the slider, for example an annular disk. When the armature plate approaches the overtravel stop, a hydraulic damping chamber is produced between the faces of the armature plate and the overtravel stop, which face each other. The fuel contained in the damping chamber generates a force which counteracts the movement of the armature plate, so that the post-oscillation of the armature plate is strongly damped.
In the known solenoid valves, the precise setting of the maximum slide path which is to be available to the armature plate on the armature pin is problematic. The maximum slide path, also called overtravel, is set by replacing the overtravel disk, through additional spacer disks, or by grinding down the overtravel stop. Since these achievements of the object require setting which is to be performed incrementally, they are costly and difficult to automate and lengthen the machining periods in manufacturing.
The solenoid valve according to the present invention having the characterizing features of claim 1 avoids the disadvantages arising in the related art. Through the arrangement of an actuator, which is arranged on a section of the armature plate facing away from the electromagnet and is adjustable in the sliding direction of the armature plate relative to the face of the armature plate facing the electromagnet, the maximum slide path of the armature plate on the armature pin may advantageously be set very easily, without parts having to be replaced or ground down multiple times. A setting procedure which includes multiple steps may be dispensed with. The achievement of the object proposed is particularly usable in a cost-effective way in automated serial production.
Advantageous embodiments and refinements of the present invention are made possible through the features contained in the sub-claims.
Therefore, the damping device may advantageously be formed by a hydraulic damping chamber between a face of the actuator and a face, which faces the face of the actuator, of the stationary part of the damping device fixed in the housing of the solenoid valve. The actuator may have, on its face facing the stationary part, an axial through-opening for passing through the armature pin.
It is particularly advantageous to arrange the actuator adjustably on the armature plate via a thread. By rotating the actuator when the armature plate is fixed or by rotating the armature plate when the actuator is fixed, the maximum slide path of the armature plate on the armature pin may be set precisely in a simple way.
The actuator is preferably implemented as a screw element provided with an internal thread, which is screwed onto a section of the armature plate. penetrated by the armature pin and provided with an external thread.
The precision of the setting results in this case from the thread pitch. The axial adjustment path of the actuator in relation to the face of the armature plate facing the electromagnet is advantageously implemented as less than half a millimeter for one full rotation of the actuator. The very flat thread pitch advantageously causes self locking of the thread, so that the actuator is fixed in its limit position. The actuator may additionally be lockable in the set position on the armature plate.
In an exemplary embodiment which is particularly easy to assemble, the return spring is supported on one end in the housing of the solenoid valve and on the other end against the actuator.